Power modules have been used in all scenes from power generation and power transmission to effective use and regeneration of energy. In manufacturing such a semiconductor device, first, a silicon wafer formed with circuits is finely cut to form silicon (Si) chips (integrated circuit (IC) chips). This cut state is referred to as dice. The die is fixed at a predetermined position of a lead frame. This process is referred to as die bonding.
In semiconductor elements including power modules, miniaturization has been being advanced. In proportion as heat generation density increases, the quality of a die bonding portion (the presence or absence of a void and/or an unbonded portion) gives a large influence on heat dissipation properties. Hereafter, it is conceivable that a reduction in thickness of the IC chip will be advanced for higher efficiency. Diffusion of heat by the semiconductor element itself is difficult; and thus, it is conceivable that the quality of the die bonding portion gives a remarkable influence by the heat dissipation properties.
In order to suppress the occurrence of the void and/or the unbonded portion in the die bonding, an expensive system such as a vacuum soldering system is used. A process such as performing scrub, which is large in the number of processes, is also used; however, the occurrence of the void is not basically solved. In a high-performance silicon carbide (SiC) semiconductor, securement of the heat dissipation properties at the die bonding portion will be more important than ever before due to becoming high in operating temperature.
Patent Document 1 proposes a method in which the bottom of a heat sink is processed into a pyramid shape to facilitate the escape of a void during soldering. Machining of the backside (die bonding surface) is difficult to perform with respect to a fragile Si chip with a thickness of 100 μm, and processing strain gives an influence on reliability even when the machining can be performed.
Patent Document 2 proposes a method in which solder is once pressed to expand to 50 to 90% of a bonding area and then the solder is made to melt to perform die bonding. As long as the total amount of solder material serving as bonding material is melted like the method disclosed in this document, the occurrence of a large void is unavoidable even when scrub is performed.
Patent Document 3 proposes a method in which pads divided by slits are formed on a bonding surface and high temperature solder is supplied thereto respectively. A slit portion is completely an unbonded portion. In the case where heat generation is large and diffusion of the heat cannot be expected due to a reduction in thickness of a chip, the slit portion causes thermal damage.